Polymorphic forms of 6-[4-(1-cyclohexyl-1H-tetrazol-5-yl)butoxy]-3,4-dihydro-2(1H)-quinolinone

ABSTRACT

Polymorphs Form B, Form C, and amorphous of 6-[4-(1-cyclohexyl-1H-tetrazol-5-yl)butoxy]-3,4-dihydro-2(1H)-quinolinone, commonly known as cilostazol, have been identified. These polymorphs may be formed in pure form, in combination with each other, in combination with other polymorphs of cilostazol, or together with other pharmaceutical agents. Processes for preparing these polymorphs, and combinations of these polymorphs, as well as methods of use and unit dosages of these polymorphic forms, and their combinations, are described.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to compositions and methods ofpreparing novel forms of the free base of6-[4-(1-cyclohexyl-11H-tetrazol-5-yl)butoxy]-3,4-dihydro-2(1H)-quinolinone(hereinafter referred to by its generic name “cilostazol”). Moreparticularly, novel crystalline forms of cilostazol, in the form ofpolymorphs B, C, and amorphous are disclosed. Most particularly, suchforms of cilostazol, individually and in combinations thereof, with andwithout polymorphic Form A, are useful in pharmaceutical formulationsand methods for using such polymorphs and formulations therof.

[0003] 2. Description of Related Art

[0004] The compound6-[4-(1-cyclohexyl-11H-tetrazol-5-yl)butoxy]-3,4-dihydro-2(1H)-quinolinoneis generally known as the pharmaceutically active compound cilostazol.Cilostazol has been known to have a singular crystalline form (Form A),which is a free base and used as an active pharmaceutical ingredient(API) for use in the preparation of drug products.

[0005] Cilostazol has the following chemical structure:

[0006] Cilostazol, and several of its metabolites, are known inhibitorsof phosphodiesterase and, more particularly, phosphodiesterase III. As aphosphodiesterase inhibitor (type III), cilostazol suppresses plateletaggregation and also acts as a direct arterial vasodilator. In additionto its reported vasodilator and antiplatelet effects, cilostazol hasbeen proposed to have beneficial effects on plasma lipoproteins,increasing plasma high density lipoprotein cholesterol andapolipoprotein (See e.g., Dawson et al., Circulation 98: 678-686 [1998];Elam et al., Arterioscler Thromb. Vasc. Biol. 18: 1942-1947[1998]; DrugEvaluation Monographs, vol. 99, Micromedex Inc.). Additionally,cilostazol has been reported as useful for the treatment of sexualdysfunction in U.S. Pat. No. 6,187,790 to Cutler. Cilostazol free baseis the API in the pharmaceutical drug product marketed under thetrademark PLETAL® (Otsuka America Pharmaceutical, Inc., Rockville, Md.;and Pharmacia Company, Kalamazoo, Mich.).

[0007] Methods of preparation of cilostazol are set forth by Nishi etal. (Chem. Pharm. Bull. 31: 1151 [1983], and U.S. Pat. No. 4,277,479,the disclosure of both references are hereby incorporated by reference,and its pharmacology, metabolism, mechanism of action and clinicalevaluations are described in Arzneimittel-Forsch. 35: 1117-1208 (1985).

[0008] Use of cilostazol in pharmaceutical formulations has been limitedby its low aqueous solubility and low bioavailability, which impede itsefficient therapeutic use. Therefore, it would be beneficial ifpharmaceutical chemists could provide a more soluble and, thus, morebioavailable drug product. These forms could lead to lower doses of drugsubstance (per unit dose and per day) required to be administered toprovide similar efficacy and, potentially, a better safety profile, topatients in need of treatment. To date, no such forms have beenprepared.

[0009] Polymorphic forms of the same drug substance or API, asadministered by itself or formulated as a drug product (also known asthe final or finished dosage form), are well known in the pharmaceuticalart to affect, for example, the solubility, stability, flowability,fractability, and compressibility of drug substances and the safety andefficacy of drug products (see, e.g., Knapman, K. Modern DrugDiscoveries, March, 2000: 53). So critical are the potential effects ofdifferent polymorphic forms in a single drug substance on the safety andefficacy of the respective drug products(s) that the United States Foodand Drug Administration (FDA) requires each drug substance manufacturer,at least, to control its synthetic processes such that the percentagesof the various respective polymorphic forms, when present, must becontrolled and consistent among batches and within the drugsubstance/product's specification as approved by the FDA.

SUMMARY OF THE INVENTION

[0010] Form A is the material produced using the methods described inU.S. Pat. No. 4,277,479 (hereinafter referred to as “the '479 patent”),and is clearly distinguishable from other polymorphic forms of thepresent invention by X-ray powder diffraction and other methods of solidstate characterization. Form A, the sole, previously known form ofcilostazol, as prepared by the procedures described in the '479 patent,has been found to have low aqueous solubility and low bioavailability.As such, Form A is not particularly well suited for commercial use inpharmaceutical formulations or for therapeutic use.

[0011] A novel crystalline form of cilostazol, Form B, which possessesdistinct advantages over the previously known Form A of cilostazol hasnow been prepared and characterized. In accordance with the presentinvention, a newly discovered polymorph, Form B of cilostazol, can beobtained in a pure form or in combination with other polymorphic formsof cilostazol. Form B is stable, and can be prepared free fromcontamination by solvates such as water or organic solvents such as, forexample, acetonitrile. As such, Form B is useful for the commercialpreparation of pharmaceutical formulations such as tablets and capsules.

[0012] Another novel crystalline form of cilostazol, Form C, that hasalso been prepared and characterized, possesses distinct advantages overthe previously known Form A of cilostazol, and is clearlydistinguishable from other polymorphic forms of the present invention byX-ray powder diffraction and other methods of solid-statecharacterization. In accordance with the present invention, Form C ofcilostazol, can be obtained in a pure form or in combination with otherpolymorphic forms of cilostazol. Form C is stable, and can be preparedfree from contamination by solvates such as water or organic solventssuch as, for example, acetonitrile. As such, Form C is also useful forthe commercial preparation of pharmaceutical formulations such astablets and capsules.

[0013] Another polymorphic form, amorphous cilostazol, has also beenprepared and characterized. Such amorphous is clearly distinguishablefrom Form A and other polymorphic forms of cilostazol by X-ray powderdiffraction and other solid-state methods of characterization. Inaccordance with the present invention, the newly discovered amorphouscilostazol can be obtained in a pure form or in combination with otherpolymorphic forms of cilostazol. Amorphous cilostazol can also beprepared free from other polymorphic forms of cilostazol andcontamination by solvates such as water or organic solvents such as, forexample, acetonitrile. As such, amorphous cilostazol may be used forcommercial pharmaceutical formulations such as tablets and capsules, butis preferably used as an intermediate for the preparation of otherpolymorphic forms of cilostazol.

[0014] Accordingly, it is an object of the present invention to providenovel compositions pharmaceutical formulations, and methods of using thenovel polymorphic forms of the present invention, and combinationsthereof.

[0015] The present invention provides novel pure and combinations ofpolymorphic forms of cilostazol, each of which are useful for providingmore desirable solubility and improved bioavailability characteristics,particularly when administered in pharmaceutical dosage forms.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 shows an ORTEP drawing of the single crystal structure ofForm A cilostazol;

[0017]FIG. 2 shows an ORTEP drawing of the single crystal structure ofForm C cilostazol;

[0018]FIG. 3 illustrates a Differential Scanning Calorimetry (DSC)thermogram for Form A cilostazol;

[0019]FIG. 4 illustrates a DSC thermogram for Form B cilostazol;

[0020]FIG. 5 illustrates a DSC thermogram for Form C cilostazol;

[0021]FIG. 6 illustrates a DSC thermogram for the combination of Forms Aand B cilostazol;

[0022]FIG. 7 illustrates a DSC thermogram for the combination of Forms Band C cilostazol;

[0023]FIG. 8 illustrates a DSC thermogram for the combination of FormsA, B and C cilostazol;

[0024]FIG. 9 illustrates an X-ray powder diffraction (XRD) pattern forForm A cilostazol;

[0025]FIG. 10 illustrates an XRD pattern for Form B cilostazol;

[0026]FIG. 11 illustrates an XRD pattern for Form C cilostazol;

[0027]FIG. 12 illustrates an XRD pattern comparing Form A cilostazol,Form B cilostazol and Form C cilostazol;

[0028]FIG. 13 illustrates an XRD pattern for amorphous cilostazol;

[0029]FIG. 14 illustrates an XRD pattern for the combination of Form Acilostazol (minor) and Form B cilostazol (major);

[0030]FIG. 15 illustrates a Fourier Transform Infrared Spectroscopy(FTIR) spectrum for Form A cilostazol;

[0031]FIG. 16 illustrates a FTIR spectrum for Form B cilostazol;

[0032]FIG. 17 illustrates a FTIR spectrum for Form C cilostazol;

[0033]FIG. 18 illustrates a FTIR spectrum overlaying Form A cilostazol,Form B cilostazol and Form C cilostazol;

[0034]FIG. 19 illustrates a FTIR spectrum for amorphous cilostazol; and,

[0035]FIG. 20 illustrates a Fourier Transform Raman Spectroscopy(FT-Raman) spectrum for Form A cilostazol;

[0036]FIG. 21 illustrates a FT-Raman spectrum for Form B cilostazol;

[0037]FIG. 22 illustrates a FT-Raman spectrum for Form C cilostazol;

[0038]FIG. 23 illustrates a FT-Raman spectrum for Form A cilostazol,Form B cilostazol and Form C cilostazol;

[0039]FIG. 24 illustrates a FT-Raman spectrum for amorphous cilostazol;and,

[0040]FIG. 25 illustrates a HPLC chromatographic overlay comparingvarious combinations of crystalline polymorphic forms of cilostazol.

DETAILED DESCRIPTION OF THE INVENTION

[0041] Preparation of Form A cilostazol,6-[4-(1-cyclohexyl-1H-tetrazol-5-yl)butoxy]-3,4-dihydro-2(1H)-quinolinone,is described in U.S. Pat. No. 4,277,479, the disclosure of such patentis herein incorporated by reference. The present invention is directedto polymorphic Form B of cilostazol, Form C of cilostazol, amorphouscilostazol, and combinations thereof, the preparation thereof,pharmaceutical formulations thereof, and the use of such polymorphs,preferably in pharmaceutical formulations, for the therapeutic treatmentof subjects in need of treatment. The polymorphic forms of the presentinvention were characterized using differential scanning calorimetry(DSC), X-ray powder diffraction (XRD), Fourier Transform InfraredSpectroscopy (FTIR), and Fourier Transform Raman Spectroscopy (FT-Raman)analysis as discussed below. Characterization with any of these methodsreveals distinctive peaks for each particularly polymorphic form,whether in a pure state or not. For example, pure Form B provides adistinct range of significant peaks when analyzed by XRD. Thesesignificant peaks will be present with XRD analysis for pure Form B aswell as for samples containing Form B in combination with otherpolymorphic forms of cilostazol.

[0042] As seen in FIGS. 1 and 2, as ORTEP drawings of the single crystalstructures of Form A of cilostazol and Form C of cilostazol,respectively, show the different orientations of the two cilostazolmolecules, thereby distinguishing these two forms of cilostazol. TheORTEP drawings are generated from the Oak Ridge Thermal EllipsoidProgram developed by Oak Ridge National Laboratory in Oak Ridge, Tenn.X-ray single crystal structural analysis was not performed on Form Bbecause of the microcrystalline nature of these samples, or amorphouscilostazol because of the non-crystalline nature thereof.

[0043] X-ray single crystal unit cell parameters for Form A ofcilostazol and Form C of cilostazol are compared in Table 1, below:TABLE 1 X-Ray Single Crystal Unit Cell Parameters for Form A and Form CForm A Form C Crystal Lattice Orthorhombic Monoclinic Space Group PbcaP2₁/n a 11.3245(4) Å 5.1476(1) Å b 9.8527(2) Å 10.7391(2) Å c35.0093(12) Å 35.2786(7) Å α 90° 90° β 90° 94.070(1)° γ 90° 90° V(Å³)3906.2(4) Å³ 1945.3(1) Å Z 8 4

[0044] Characterization of Form A of cilostazol, Form B of cilostazol,and Form C of cilostazol was further completed using DSC thermograms,shown in FIGS. 3, 4, and 5, respectively, with DSC thermograms forcombinations of Form A and Form B; Form B and Form C; and Forms A, B,and C are shown in FIGS. 6, 7, and 8 respectively.

[0045] DSC data were generated using a Mettler-Toledo DSC 821^(e)(Columbus, Ohio) with a Julabo FT900 intercooler chiller (JulaboCompany; Allentown, Pa.). In general, samples were analyzed in a vented,sealed aluminum pan. Because the endothermic peak may vary dependingupon the rate of heating and the calibration and precision of theinstrument, with the amount of peak variation dependent upon the heatingrate used, all thermograms included herein were run under the same,consistent conditions: heating at 10° C. per minute under a nitrogenpurge at 40 mL/minute.

[0046] As seen in FIG. 3, the DSC thermogram for Form A gives anendothermic peak at about 162° C. (onset at about 160° C.). The DSCthermogram shown in FIG. 4 shows an endothermic peak for Form B at about139° C. (onset at approximately 136° C.). In FIG. 5, the DSC thermogramfor Form C also shows an endothermic peak at about 149° C. (onset atabout 146° C.).

[0047] The DSC thermogram in FIG. 6 shows several heat cycles of acilostazol sample, with both Form A and Form B of cilostazol present inthe third heat cycle. At the bottom of the thermogram, Form A ofcilostazol appears during the first heating cycle at about 162° C.Typically, the maximum temperature used for the first heating cycle wasfrom about 180° C. to about 200° C. and, more typically about 200° C. Inthis instance, after reaching a temperature of about 200° C., thecilostazol was then cooled to about 0° C., which is shown in the firstcooling cycle of the DSC thermogram (immediately above the first heatingcycle). Once the cilostazol sample reached approximately 0° C., it wasimmediately reheated to about 130° C., shown in the second heating cycleof the DSC thermogram. During this reheating of the cilostazol sample,the sample appears to pass through a glass transition at about 35° C.(onset at about 32° C.), with an exotherm occurring at about 104° C.(onset at about 90° C.). After this reheating, the sample was placedthrough a second cooling cycle (recooling) to about 0° C., and againreheated in a third heating cycle shown at the top of the DSCthermogram. During the third heating cycle, both Form B and Form Aappear, with Form B appearing at about 138° C. (onset at about 135° C.)during this third heating cycle, and Form A appearing at approximately161° C. (onset at about 159° C.).

[0048]FIG. 7 shows a DSC thermogram for the combination of Forms B andForm C in the third heating cycle. The DSC thermogram in FIG. 7 showsseveral heat cycles using Form A as the starting material. Afterreaching a temperature of about 200° C. in the first heating cycle, thesample was then cooled to about 0° C. Once the cilostazol sample reachedabout 0° C., it was immediately reheated to about 100° C., and held atthis temperature for about 5 minutes. During this reheating, thecilostazol sample passed through the glass transition temperature atabout 35° C. (onset at about 32° C.), but was not permitted tocompletely proceed through the exotherm which typically starts at about84° C. by beginning the recooling stage once the temperature reachedabout 100° C. and held for about 5 minutes. This step is critical forthe formation of at least some Form C, which is necessary for preparingpure Form C as taught herein below. After this reheating the sample wasplaced through a second cooling cycle to approximately 0° C., and againreheated in a third heating cycle as shown at the top of the DSCthermogram. During the third heating cycle, both Form B and Form C aremelted, with Form B melting at about 138° C. (onset at about 135° C.),and Form C melting at about 149° C. (onset at about 147° C.). The peaksshow a Form B to Form C peak area ratio of approximately 4:3,respectively, with the relative amount of Form B and Form C furthervariable on the heat of enthalpy of each polymorphic form.

[0049]FIG. 8 illustrates a DSC thermogram for the combination of Form A,Form B and Form C having a second heating cycle with a maximumtemperature of about 110° C. with a holding time of about 30 minutes.The peaks in the third heating cycle show a Form A to Form B to Form Cpeak area ratio of approximately 8:2:1, respectively, with the relativeamount of Form A, Form B and Form C further variable on the heat ofenthalpy of each polymorphic form. This thermogram shows Form B and FormC having a lower melting point than Form A, indicating that the crystalpacking forces for Forms B and C are not as great as Form A these datastrongly suggest that Form B and Form C are more soluble than Form A ofcilostazol.

[0050] In FIGS. 9, 10 and 11, the XRD patterns for Form A, Form B andForm C, respectively, are shown, with the three XRD patterns overlayedfor comparison in FIG. 12. As seen in FIG. 12, the XRD patterns of FormA, Form B and Form C of cilostazol demonstrate three distinctcrystalline forms of the cilostazol, evidencing pure Form B and pureForm C. Characterization of amorphous cilostazol was also performed, asseen in the XRD pattern for amorphous cilostazol in FIG. 13. XRD wasperformed using a Siemens D500 Diffractometer (Madison, Wis.). Sampleswere analyzed from 2-40° in 2θ at 2.4°/minute using CuKα (50 kV, 30 mA)radiation on a zero-background sample plate.

[0051] Tabulations of the peak positions from the X-ray powder patternsfor Form A, Form B and Form C are listed in Tables 2, 3 and 4,respectively, below. It is well known by one of ordinary skill in theart that lot-to-lot variations of crystal shape and/or size, as well asvariations among instruments and calibration of such instruments, canappear as preferred orientation in the X-ray powder diffractionpatterns. This preferred orientation can be seen as variations in therelative intensities of the peaks, such variations in an amount of up toabout 20%. TABLE 2 X-Ray Powder Diffraction Significant Peaks of Form Aof Cilostazol 2-Theta (degrees) d(Å) Strength¹ I% 5.2 16.89 vw 1.6 9.49.40 m 9.3 10.3 8.59 m 9.4 12.9 6.86 vs 100.0 14.2 6.21 w 3.6 15.3 5.79s 27.0 15.8 5.59 s 31.3 16.6 5.34 w 2.7 17.2 5.15 w 3.8 18.1 4.91 w 3.518.8 4.72 m 10.7 19.4 4.56 m 9.0 20.4 4.36 m 16.3 20.8 4.27 m 9.9 21.54.13 vw 1.2 22.0 4.03 m 9.9 22.2 3.99 w 7.6 23.5 3.78 m 15.7 24.2 3.67 w4.4 25.0 3.56 w 3.6 25.5 3.49 w 5.7 25.8 3.46 w 7.0 25.9 3.43 w 4.3 27.43.25 w 3.2 28.3 3.15 vw 0.6 28.4 3.14 vw 0.9 29.4 3.04 w 2.6 30.1 2.97vw 1.1 31.7 2.82 m 13.3 32.1 2.78 vw 1.5 33.4 2.68 vw 1.9 33.9 2.64 vw1.1 34.6 2.59 vw 0.6 35.0 2.56 vw 0.5 36.0 2.50 vw 6.5 38.2 2.35 vw 0.739.1 2.30 vw 1.2 39.5 2.28 vw 0.9

[0052] TABLE 3 X-Ray Powder Diffraction Significant Peaks of Form B ofCilostazol 2-Theta (degrees) d(Å) Strength¹ I% 9.8 9.03 w 2.2 10.7 8.29s 35.7 11.2 7.89 vw 1.9 13.4 6.61 vw 0.9 14.2 6.23 s 22.4 14.7 6.03 m15.9 15.8 5.60 s 20.9 16.6 5.33 m 10.6 17.7 5.02 w 2.2 17.9 4.95 m 8.018.8 4.72 s 33.9 19.7 4.50 w 7.1 20.4 4.35 s 40.4 21.6 4.10 vs 100.022.4 3.96 m 13.7 22.8 3.90 m 20.0 23.5 3.78 m 17.2 24.7 3.61 w 5.3 24.83.58 m 9.9 25.9 3.43 s 48.0 26.8 3.32 m 8.1 27.7 3.22 w 4.0 28.5 3.13 w7.1 29.2 3.06 w 4.7 29.7 3.01 m 10.1 30.2 2.96 m 12.9 30.7 2.91 m 8.731.2 2.86 w 6.7 31.6 2.83 w 4.2 32.3 2.77 vw 1.7 32.6 2.74 w 2.2 33.02.71 vw 0.9 33.5 2.68 w 4.3 33.8 2.65 w 3.8

[0053] TABLE 4 X-Ray Powder Diffraction Significant Peaks of Form C ofCilostazol 2-Theta (degrees) d(Å) Strength¹ I% 5.0 17.51 w 0.8 8.6 10.22s 10.1 9.7 9.12 vw 9.3 10.1 8.75 vw 8.3 13.1 6.78 s 12.3 15.1 5.85 m 2.316.7 5.29 s 15.1 17.3 5.12 m 27.7 18.2 4.86 w 5.6 19.4 4.56 m 12.3 20.24.40 s 11.4 20.9 4.25 w 6.7 21.1 4.21 w 7.2 21.9 4.07 vw 1.1 22.5 3.95vw 1.4 23.7 3.75 vs 100.0 24.3 3.66 w 2.5 24.8 3.58 w 4.8 25.7 3.46 s25.9 26.1 3.41 w 4.0 27.1 3.29 w 3.0 27.8 3.21 vw 1.0 29.0 3.08 vw 0.929.2 3.05 vw 0.6 29.8 3.00 vw 1.7 30.5 2.92 vw 1.4 31.7 2.82 vw 0.7 32.52.76 w 4.1 33.5 2.68 w 3.6 33.9 2.64 vw 1.6 34.9 2.57 vw 0.6 36.2 2.48vw 0.5 37.4 2.40 vw 0.3 38.0 2.36 vw 0.5 39.2 2.30 vw 0.5

[0054] The XRD peaks shown in Table 2, demonstrated that the significantpeaks of Form A (greater than 8%) are typically located at two-theta(20) angles of about 9.4, 10.3, 12.9, 15.3, 15.8, 18.8, 19.4, 20.4,20.8, 22.0, 23.5 and 31.7°. For Form B, the significant XRD peaks (shownin Table 3) are at two-theta (2θ) angles of about 10.7, 14.2, 14.7,15.8, 16.6, 17.9, 18.8, 20.4, 21.6, 22.4, 22.8, 23.5, 24.8, 25.9, 26.8,29.7, 30.2, and 30.7°. For Form C, the significant XRD peaks (shown inTable 4) are at two-theta (2θ) angles of about 8.6, 9.7, 10.1, 13.1,16.7, 17.3, 19.4, 20.2, 23.7 and 25.7°.

[0055] The XRD pattern for the combination of a minor (approximately10%) amount of Form A of cilostazol and a major (approximately 90%)amount of Form B of cilostazol is shown in FIG. 14.

[0056] The FTIR spectrum for Form A, Form B and Form C, are shown inFIGS. 15, 16, and 17, respectively and an overlay of the three spectraare shown in FIG. 18. The FTIR spectrum for amorphous cilostazol isshown in FIG. 19. FTIR was performed using a Nicolet Nexus 670 FTIRspectrometer with a Micro-FTIR attachment (Silicon ATR). Analysis wasgenerally performed on neat samples at 4 cm⁻¹ resolution, collecting 64scans from 4000-650 cm⁻¹. The major bands of the FTIR spectra of Form A,Form B, and Form C are tabulated in Table 5, below: TABLE 5 Major FTIRpeaks of Form A, Form B, Form C and Amorphous Cilostazol (cm⁻¹) Form AForm B of of Form C of Amorphous cilostazol cilostazol cilostazolcilostazol 3180 3181 3191 3210 3046 3054 3056 3063 2937 2940 2938 29342872 2868 2870 2861 1667 1662 1674 1672 1505 1504 1504 1504 1431 14431430 1421 1402 1393 1398 1381 1244 1240 1243 1240 1197 1205 1187 11951156 1162 1154 1156 1128 1124 1126 1130 1039 1030 1036 1026 846 842 864863 675 658 674 670

[0057] The polymorphic forms of cilostazol are further characterized inFIGS. 20, 21,22, and 24 for Form B, Form C, and amorphous cilostazolrespectively. FT-Raman was performed using a Nicolet Nexus 670 FTIRspectrometer with a FT-Raman attachment. Samples were generally analyzedneat at 8 cm⁻¹ resolution, collecting 100 scans from 3800-100 cm⁻¹ witha laser wattage of approximately 1W. Major spectral bands of theFT-Raman for the Form A, Form B, Form C and amorphous cilostazol arelisted in Table 6, below: TABLE 6 Major FT-Raman peaks of Form A, FormB, Form C (cm⁻¹) and Amorphous Cilostazol Form A Form B Form C of of ofAmorphous cilostazol cilostazol cilostazol cilostazol 3056 3054 30513059 2954 2941 2939 2940 2927 2914 2900 2905 2871 2868 2869 2861 16261616 1627 1618 1592 — 1593 1594 1505 1506 1503 1506 1452 1443 1447 14451428 1422 1425 1420 1385 1386 1386 1387 1329 1334 1324 1328 1309 13081308 1303 1278 1271 1274 1277 1253 1246 1255 1247 1056 1057 1052 10531034 1030 1031 1028 1012 1013 1008 1007 875 890 873 872 861 856 861 858824 824 817 819 773 776 777 776 741 735 740 739 675 660 676 675 594 590592 592 565 562 566 561 527 525 535 530 420 409 418 418 384 383 379 384277 280 276 275

[0058] The HPLC Chromatogram of Form A was overlayed with thechromatograms of a combination of polymorphic Form B and Form C, and thechromatogram of a combination of polymorphic Form A with Form B and FormC as shown in FIG. 25. This overlay demonstrates the purity and identityof each polymorphic combination to be as the same compound in solution(i.e., no degradation occurred in the thermal processing of thecilostazol) with a total amount of impurities of less than about 0.1% ineach polymorphic combination.

[0059] Accordingly, the amorphous, Form B, and Form C polymorphic formsof cilostazol have been characterized as distinct from Form A, and fromeach other. X-ray single crystal structural analysis, DSC, XRD, FTIR,and/or FT-Raman confirm the existence of the novel Form B of cilostazol,Form C, and amorphous cilostazol, and other various combinations ofpolymorphic forms of the present invention.

[0060] In preparing amorphous cilostazol, any polymorphic form orcombination of polymorphs of cilostazol (preferably Form A) is used as astarting material. The starting material is heated sufficiently formelting. Typically, when the heating rate is held constant at about 10°C./minute Form A of cilostazol melts at a temperature at about 160° C.Thus, temperatures from about 170° C. or greater (preferably up to about200° C.) are used to ensure complete melt of the cilostazol startingmaterial. Excessive temperatures that may alter the chemicalcharacteristics, (e.g., cause degradation) of the cilostazol moleculesare not used. As such, representative melting temperatures range fromabout 170° C. to about 200° C. Heating rates include any controllableheating process for complete melting of the cilostazol startingmaterial. Representative static or variable heating rates include, forexample, from about 5° C. per minute, 10° C. per minute, 15° C. perminute, 50C per minute, and other such rates. An inert atmosphere, suchas for example, a nitrogen atmosphere or, preferably, nitrogen purge,should be used to reduce or eliminate potential oxidative reactionsduring the melting of the cilostazol.

[0061] The melted cilostazol is cooled from its molten state to aboutambient temperature or below to provide amorphous cilostazol. Thecooling steps described herein were all run at a cooling rate at about10° C./minute using the aforementioned Julabo FT900 intercooler chiller.The cilostazol sample should be maintained free of debris, such as dustand other foreign material and contaminates, and/or mechanical shockthat would induce nucleation sites within the cilostazol sample. Ratesof cooling are controlled to minimize thermal shock and performed in amanner to minimize contaminates and/or mechanical shock to thecilostazol which could induce nucleation sites which can inducecrystallization. Typically, this will result in the formation Form Acilostazol. Representative cooling rates include, for example, fromabout 1° C. per minute, 5° C. per minute, 10° C. per minute, 15° C. perminute, 50° C. per minute, and other such rates.

[0062] The identical steps of melting and cooling as described above areused for forming amorphous cilostazol are used for preparing Form Band/or Form C of cilostazol.

[0063] The samples are cooled for the formation of Form B and/or Form C,by reducing the temperature of the sample to about or below the glasstransition temperature of cilostazol (about 32° C.). Cooling suchsamples only to temperatures greater than about 32° C. can provide suchpolymorph formation, primarily Form B, but the resulting materialtypically is of significantly lower purity. Because this cooling stepcan significantly affect the purity of the polymorph(s) formed insubsequent steps, the temperature of the melted cilostazol is cooled toa temperature of about 0° C. or less, and more preferably totemperatures of from about 0° C. to about −20° C. A preferred coolingrate is about 10° C./minute.

[0064] The next step, reheating of the cooled sample, is the step thatcontrols the formation of Form B, Form C, and various combinations ofthe polymorphic forms of cilostazol. Typically, three primary variablesare responsible for such formation including: heating rate, maximumtemperature (heating temperature), and holding time (collectively, the“heating variables”). One of ordinary skill in the art will recognizethat the change of one heating variable will affect one or both of theother heating variables. It is important to note that maximumtemperature refers to the heating temperature of the entire, respectivesample, and hold time commences upon such entire sample reaching thedesired heating temperature. For example, when the heating rate is heldconstant, an increase in the heating temperature will typically permit areduction in the hold time while the same, desired polymorph orcombination of polymorphs, is formed. Accordingly, the teachings hereinare intended to demonstrate the preparation of the cilostazol polymorphsof the present invention but, in no way, should be construed as limitingto the scope and breadth of the present invention.

[0065] Heating rates are controlled in a manner to systematically impartenergy into the cilostazol sample. Representative heating rates includefrom about 1° C. per minute, 5° C. per minute, 10° C. per minute, 20° C.per minute, 50° C. per minute, and the like. However, it is best tomaintain the heating rate constant at a rate of about 5° C. to about 20°C. per minute, and more preferably at about 10° C. per minute.

[0066] For the preparation of Form B, when holding the heating rateconstant, as temperatures are increased, the percent of Form B isgenerally increased compared to other polymorphic forms as determined bythe DSC methods taught herein. For example, when the cooled sample isheated to a temperature of 80° C., the sample primarily remainsamorphous cilostazol, generally, because the energy required to formcrystalline polymorphic cilostazol is insufficient, particularly whenthe heating hold time is negligible. Similarly, holding the heating rateconstant and a hold time of about zero minutes, samples heated to about90° C. to about 105° C. typically contain a combination of Form B andamorphous cilostazol at varying percentages of each. However, some FormC and, potentially, Form A, may be crystallized using these heatingtemperatures when the heating rate is held constant as taught hereinand, at a hold time of about zero minutes. As heating temperature isincreased above 105° C., the purity of Form B is increased. For example,a temperature of about 120° C., hold time of about zero minutes, andheating rate of about 10° C./minute provides pure Form B (withindetectable limits). Temperatures above about 130° C. will initiatemelting of the resulting Form B polymorph.

[0067] Alternately, when maintaining a constant heating rate of about110° C./minute, lower temperatures can be employed using longer holdtimes. For example, with temperatures below about 105° C., hold times ofabout 5 minutes and greater will provide purities of Form B similar topurities obtained with heating temperatures greater than about 105° C.with hold times of about zero minutes. Depending upon the heatingvariables used, more particularly, holding the heating rate constant,with a heating temperature of about 100° C., a hold time of about 5minutes essentially eliminates amorphous cilostazol. Under theseconditions the resulting product is predominately Form B, with theremaining portion being predominately Form C.

[0068] Moreover, pure Form B can also be formed by using heatingtemperatures greater than about 100° C. and, for small samples increasedhold times. For examples when maintaining a constant heating rate ofabout 10° C. per minute, a heating temperature of about 110° C. and holdtime of about 5 minutes also provides pure Form B. Other variations ofthe heating variables will also provide pure Form B providing theheating temperature does not exceed the melting point of Form B and thetemperature is held for a time period sufficient to complete theformation of pure Form B of the present invention. As such, the scope ofthe present invention is not limited to these exemplifications.

[0069] After the heating step is completed and the desired polymorphicform(s) are obtained, the resulting cilostazol is recooled. With regardto Form B, the cilostazol is actively recooled or allowed to passivelyrecool, preferably at a controlled rate (preferably about 10°C./minute), to about ambient temperature.

[0070] Preferably, Form B is produced in a pure form (devoid ofdetectable amounts of other polymorphic forms of cilostazol asdetermined by FTIR, FT-Raman and/or X-Ray powder diffraction, asappropriate), or in substantially pure form having negligible otheramounts of detectable polymorphic forms of cilostazol.

[0071] For the preparation of pure Form C of the present invention, theheating step for the preparation of Form B as described herein is usedproviding at least some Form C (as detected using DSC) is present in thesample. It is preferred to use a sample that has a higher rather thanlower percentage of Form C. For example, the heating step for thepreparation of Form B above wherein the heating rate is held constant, aheating temperature of about 100° C., and hold time of about 5 minutesprovides a good starting material for the preparation of pure Form C.

[0072] Following such heating step, the sample is actively recooled,preferably in a controlled manner, to about ambient temperature orbelow. Preferred cooling temperatures are from about ambient temperatureto about −80° C., and more preferred from about −10° C. to about 10° C.

[0073] For the preparation of purer forms of Form C and, particularly,pure Form C, the recooled sample containing at least some Form C isreheated to a temperature which is greater than about the melting pointof Form B (about 135° C. to about 137° C.) but below the melting pointof Form C (about 147° C. to about 149° C.). The temperature typically isheld for a period of time that is sufficiently long to ensure thecomplete melt of Form B. Providing all Form B present is melted duringthis reheating step, pure Form C is formed during the final re-coolingstep from the melted Form B, using the remaining, un-melted Form C asseed crystals for the resulting pure Form C. If the Form B crystals arenot completely melted during the re-heating step, this resultingmaterial will predominately comprise Form C with the unmelted portion ofForm B remaining as Form B. As with all of the processes set forthherein, it is preferred to maintain the rate of heating constant atabout 10° C./minute.

[0074] During the final recooling step, the cilostazol is activelyrecooled or allowed to passively recool, preferably at a controlledrate, to about ambient temperature. Preferably, Form C is produced in apure form (devoid of detectable amounts of other polymorphic forms ofcilostazol as determined by FTIR, FT-Raman, and/or X-ray powderdiffraction, as appropriate), or in substantially pure form havingnegligible amounts of other detectable polymorphic forms of cilostazol.

[0075] The present invention also provides pharmaceutical formulationscomprising pure Form B, pure Form C, or pure amorphous cilostazol,either as the sole active ingredient or in combination with other activeingredients including, for example, other polymorphic forms ofcilostazol or other pharmaceutically active agents, at least onepharmaceutically acceptable carrier, diluent, and/or excipient.Combinations of more than one polymorphic form of cilostazol areprepared via the described crystallization procedures or, for moreprecise combinations, via blending of pure or known polymorphic ratios.Preferred polymorphic combinations include, for example, Form B withForm C, Form A, and/or amorphous cilostazol; Form C with Form B, Form A,and/or amorphous cilostazol, and amorphous cilostazol with Form B, FormC and/or Form A of cilostazol.

[0076] Preferably, the novel crystalline forms of cilostazol, Form B andForm C, and amorphous cilostazol, are in pure form. Pure form includesthose samples of either Form B, Form C, or amorphous cilostazol,individually, that do not possess detectable amounts of any additionalform of cilostazol as evidenced by XRD, FTIR, and/or FT-Raman analysis.

[0077] For the most effective administration of the polymorphic forms ofthe present invention, it is preferred to prepare a pharmaceuticalformulation preferably in unit dose form, comprising one or more of theactive ingredients of the present invention and one or morepharmaceutically acceptable carrier, diluent, or excipient.

[0078] As used herein, the term “active ingredient” refers to any of theembodiments set forth herein, particularly Form B, Form C, and amorphouscilostazol, individually and in combination among polymorphic forms ofthe present invention or other cilostazol polymorphic forms. Morepreferably polymorphic Form B and Form C of the present invention areused in pure form in the pharmaceutical formulations of the presentinvention.

[0079] Preferred pharmaceutical formulations may include, without beinglimited by the teachings as set forth herein, a solid dosage form, ofForm B, Form C and/or amorphous cilostazol, of the present invention incombination with at least one pharmaceutically acceptable excipient,diluted by an excipient or enclosed within such a carrier that can be inthe form of a capsule, sachet, tablet, buccal, lozenge, paper, or othercontainer. Additionally, such pharmaceutical formulation may include aliquid formulation prepared from Form B, Form C and/or amorphouscilostazol API of the present invention in combination with at least onepharmaceutically acceptable excipient, diluted by an excipient orenclosed within an appropriate carrier. When the excipient serves as adiluent, it may be a solid, semi-solid, or liquid material which acts asa vehicle, carrier, or medium for the active ingredient(s). Thus, theformulations can be in the form of tablets, pills, powders, elixirs,suspensions, emulsions, solutions, syrups, capsules (such as, forexample, soft and hard gelatin capsules), suppositories, sterileinjectable solutions, and sterile packaged powders.

[0080] Examples of suitable excipients include, but are not limited to,starches, gum arabic, calcium silicate, microcrystalline cellulose,polyvinylpyrrolidone, cellulose, water, syrup, and methyl cellulose. Theformulations can additionally include lubricating agents such as, forexample, talc, magnesium stearate and mineral oil; wetting agents;emulsifying and suspending agents; preserving agents such as methyl- andpropyl-hydroxybenzoates; sweetening agents; or flavoring agents.Polyols, buffers, and inert fillers may also be used. Examples ofpolyols include, but are not limited to: mannitol, sorbitol, xylitol,sucrose, maltose, glucose, lactose, dextrose, and the like. Suitablebuffers encompass, but are not limited to, phosphate, citrate, tartrate,succinate, and the like. Other inert fillers which may be used encompassthose which are known in the art and are useful in the manufacture ofvarious dosage forms. If desired, the solid pharmaceutical compositionsmay include other components such as bulking agents and/or granulatingagents, and the like. The compositions of the invention can beformulated so as to provide quick, sustained, controlled, or delayedrelease of the active ingredient after administration to the patient byemploying procedures well known in the art.

[0081] In certain embodiments of the present invention, the activeingredient(s) may be made into the form of dosage units for oraladministration. The active ingredient(s) may be mixed with a solid,pulverant carrier such as, for example, lactose, saccharose, sorbitol,mannitol, starch, amylopectin, cellulose derivatives or gelatin, as wellas with an antifriction agent such as for example, magnesium stearate,calcium stearate, and polyethylene glycol waxes. The mixture is thenpressed into tablets or filled into capsules. If coated tablets,capsules, or pulvules are desired, such tablets, capsules, or pulvulesmay be coated with a concentrated solution of sugar, which may containgum arabic, gelatin, talc, titanium dioxide, or with a lacquer dissolvedin the volatile organic solvent or mixture of solvents. To this coating,various dyes may be added in order to distinguish among tablets withdifferent active compounds or with different amounts of the activecompound present.

[0082] Soft gelatin capsules may be prepared in which capsules contain amixture of the active ingredient(s) and vegetable oil or non-aqueous,water miscible materials such as, for example, polyethylene glycol andthe like. Hard gelatin capsules may contain granules or powder of theactive ingredient in combination with a solid, pulverulent carrier, suchas, for example, lactose, saccharose, sorbitol, mannitol, potato starch,corn starch, amylopectin, cellulose derivatives, or gelatin.

[0083] Tablets for oral use are typically prepared in the followingmanner, although other techniques may be employed. The solid substancesare gently ground or sieved to a desired particle size, and a bindingagent is homogenized and suspended in a suitable solvent. The activeingredient(s) and auxiliary agents are mixed with the binding agentsolution. The resulting mixture is moistened to form a uniformsuspension. The moistening typically causes the particles to aggregateslightly, and the resulting mass is gently pressed through a stainlesssteel sieve having a desired size. The layers of the mixture are thendried in controlled drying units for a pre-determined length of time toachieve a desired particle size and consistency. The granules of thedried mixture are gently sieved to remove any powder. To this mixture,disintegrating, anti-friction, and anti-adhesive agents are added.Finally, the mixture is pressed into tablets using a machine with theappropriate punches and dies to obtain the desired tablet size.

[0084] Liquid preparations for oral administration are prepared in theform of solutions, syrups, or suspensions with the latter two formscontaining, for example, active ingredient(s), sugar, and a mixture ofethanol, water, glycerol, and propylene glycol. If desired, such liquidpreparations contain coloring agents, flavoring agents, and saccharin.Thickening agents such as carboxymethylcellulose may also be used.

[0085] As such, the pharmaceutical formulations of the present inventionare preferably prepared in a unit dosage form, each dosage unitcontaining from about 10 mg to about 300 mg, preferably from about 25 mgto about 125 mg and more preferably from about 40 mg to about 110 mg ofthe cilostazol active ingredient(s). Other pharmaceutically activeagents can also be added to the pharmaceutical formulations of thepresent invention at therapeutically effective dosages. In liquid form,unit doses contain from about 10 to about 300 mg, preferably about 25 mgto about 125 mg and more preferably about 40 mg to about 110 mg of suchcilostazol active ingredient(s).

[0086] The term “unit dosage form” refers to physically discrete unitssuitable as unitary dosages for human subjects/patients or othermammals, each unit containing a predetermined quantity of activeingredient calculated to produce the desired therapeutic effect, inassociation with preferably, at least one pharmaceutically acceptablecarrier, diluent, or excipient.

[0087] The invention also provides methods of treating a subject (e.g.,mammal, particularly humans) comprising administering to a subject inneed of such treatment a therapeutically effective amount of at leastone active ingredient, formulation thereof, or unit dose forms thereof,each as described herein. The active ingredient(s) are used to inhibitcellular phosphodiesterase, particularly phosphodiesterase III. Theprimary use for such active ingredient(s) is for the reduction ofintermittent claudication in such subjects, typically manifested by anincreased walking distance. The cilostazol active ingredients of thepresent invention may also be used for the treatment of other diseasestates related to vasodilation including, for example, stroke andantiplatelet effects. Such active ingredients may also increase plasmahigh density lipoprotein cholesterol and apolipoprotein in subjects inneed of such treatment as well as being used to treat sexualdysfunction.

[0088] As used herein, the term “treatment”, or a derivative thereof,contemplates partial or complete inhibition of the stated disease statesuch as, for example, intermittent claudication, when an activeingredient of the present invention is administered prophylactically orfollowing the onset of the disease state for which such activeingredient of the present invention is administered. For the purposes ofthe present invention, “prophylaxis” refers to administration of theactive ingredient(s) to a subject to protect the subject from any of thedisorders set forth herein, as well as others.

[0089] The typical active daily dose of the cilostazol activeingredient(s) will depend on various factors such as, for example, theindividual requirement of each patient, the route of administration, andthe disease state. An attending physician may adjust the dosage ratebased on these and other criteria if he or she so desires. A suitabledaily dosage, typically administered b.i.d. in equally divided doses, isfrom about 50 mg to about 250 mg, preferably from about 80 mg to about240 mg, and more preferably from about 100 mg to about 200 mg. Apreferred range is from about 100 mg to about 200 mg total daily dose.It should be appreciated that daily doses other than those describedabove may be administered to a subject, as appreciated by an attendingphysician.

[0090] The following examples are for illustrative purposes only and arenot intended to limit the scope of the claimed invention.

EXAMPLE 1 Preparation of Pure Form B of Cilostazol

[0091] A sample of approximately 5 mg of Form A of cilostazol was placedin a vented, sealed aluminum holder and placed in a DSC furnace. Under anitrogen purge of 40 milliliters per minute, the sample was heated froma temperature of 30° C. to approximately 200° C. (past the melting pointof Form A) at a heating rate of 10° C. per minute. The molten cilostazolwas cooled within the furnace to approximately 0° C. at a cooling rateof approximately 10° C. per minute. The cooled cilostazol was reheatedfrom 0° C. to 110° C., and held at 110° C. for five minutes. Afterholding the cilostazol at 110° C. for five minutes, the cilostazol wascooled to 0° C. at a rate of 10° C. per minute. The cilostazol was thenreheated in an undisturbed state by DSC at a rate of 10° C. per minuteto a final temperature about 170° C., the sample showed an endothermicpeak for Form B of cilostazol at approximately 138° C. (onset observedat about 136° C.) with a minor peak at 149° C. which relates to Form C(onset observed at about 147° C.).

EXAMPLE 1A Preparation of Pure Form B of Cilostazol

[0092] A sample of approximately 20 mg of Form A of cilostazol wasplaced in a vented, sealed aluminum holder and placed in a DSC furnace.Under a nitrogen purge of 40 milliliters per minute, the sample washeated from a temperature of 30° C. to approximately 200° C. (past themelting point of Form A) at a heating rate of 10° C. per minute. Themolten cilostazol was cooled within the furnace to approximately 0° C.at a cooling rate of approximately 10° C. per minute. The cooledcilostazol was reheated from 0° C. to 1 10° C., and held at 110° C. forfive minutes. After holding the cilostazol at 110° C. for five minutes,the cilostazol was cooled to 30° C. at a rate of 10° C. per minute. Thesample was removed and analyzed by XRD, FTIR and FT-Raman whichconfirmed the sample as 100% Form B of cilostazol.

EXAMPLE 1B Transformation of Pure Form B of Cilostazol to Form A ofCilostazol

[0093] The resultant sample of Example 1A was disturbed with scratching,which caused the cilostazol sample to undergo a solid state phasetransformation at approximately 119° C. followed by an endotherm of meltat approximately 160° C. (Form A) during heating by DSC from 30° C. toapproximately 200° C. at 10° C. per minute.

EXAMPLE 2 Preparation of Pure/Essentially Pure Form C of Cilostazol

[0094] A sample of approximately 14 mg of Form A of cilostazol wasplaced in a vented, sealed aluminum holder and placed in a DSC furnace.Under a nitrogen purge of 40 milliliters per minute, the sample washeated from a temperature of 30° C. to approximately 200° C. (past themelting point of Form A) at a heating rate of 10° C. per minute. Themolten cilostazol was cooled to approximately 0° C. at a cooling rate ofapproximately 10° C. per minute. The cooled cilostazol was reheated from0° C. to 100° C., and held at 100° C. for five minutes. After holdingthe cilostazol at 100° C. for five minutes, the cilostazol was cooled to0° C. at a rate of 10° C. per minute. The cilostazol was then reheatedat a rate of 110° C. per minute to a temperature of 145° C. and held at145° C. for 5 minutes, after which time the cilostazol was then recooledto 0° C. at a rate of 10° C. per minute. Upon reheating in anundisturbed state, by DSC, the sample showed single endothermic peak forForm C at about 149° C. (onset of about 146° C.).

EXAMPLE 2A Preparation of Pure Form C of Cilostazol

[0095] A sample of approximately 22 mg of Form A cilostazol was placedin a vented, sealed aluminum holder and placed in a DSC furnace under anitrogen purge of 40 milliliters per minute, the sample was reheatedfrom a temperature of 30° C. to approximately 200° C. (past the meltingpoint of Form A) at a heating rate of 10° C. per minute. The moltencilostazol was cooled to approximately 0° C. at a cooling rate ofapproximately 10° C. per minute. The cooled cilostazol was reheated from0° C. to 100° C., and held at 100° C. for five minutes. After holdingthe cilostazol at 100° C. for five minutes, the cilostazol was cooled to0° C. at a rate of 10° C. per minute. The cilostazol was then reheatedat a rate of 10° C. per minute to a temperature of 145° C. and held forfive minutes, after which time the cilostazol was then recooled to 30°C. at a rate of 10° C. per minute. A single crystal was obtained fromthe DSC pan and analyzed by this technique. The structure was found tohave a different polymorphic form than that of Form A or Form B(identified in Example 1). The cilostazol sample displayed a unique XRDpowder pattern, FTIR and FT-Raman spectra and was identified as 100%Form C of cilostazol.

EXAMPLE 2B Transformation from Form C to Form A of Cilostazol

[0096] When the sample is stressed and reheated (as detailed in Example2A), the sample undergoes a solid state phase transformation atapproximately 147° C. followed by an endotherm of melt at about 160° C.(Form A) during heating by DSC from 30° C. to approximately 200° C. at10° C. per minute. This disturbance of sample is believed to inducenucleation which preferentially causes Form A of cilostazol to form uponheating.

EXAMPLE 3 Preparation of a Combination of Form B of Cilostazol and FormA of Cilostazol (About 60:40)

[0097] A sample of approximately 7 mg of Form A cilostazol was placed ina vented, sealed aluminum holder and placed in a DSC furnace under anitrogen purge of 40 milliliters per minute, the sample was heated froma temperature of 30° C. to approximately 200° C. (past the melting pointof Form A) at a heating rate of 10° C. per minute. The molten cilostazolwas cooled to approximately 0° C. at a cooling rate of approximately 10°C. per minute. The cooled cilostazol was reheated from 0° C. to 130° C.The cilostazol was then cooled to 0° C. at a rate of 10° C. per minute.

[0098] The cilostazol was then reheated in an undisturbed state by DSCfrom 0° C. to 200° C. at 10° C. per minute. Two endotherms of melt wereobserved at approximately 138° C. (Form B) and 161° C. (Form A) in aheat of enthalpy ratio of approximately 60:40, respectively, with therelative amount of Form B and Form A further variable on the heat ofenthalpy of each polymorphic form.

EXAMPLE 4 Preparation of a Combination of Form B of Cilostazol and FormA of Cilostazol (About 60:40)

[0099] A sample of approximately 6 mg of Form A cilostazol was placed ina vented, sealed aluminum holder and placed in a DSC furnace under anitrogen purge of 40 milliliters per minute, the sample was heated froma temperature of 30° C. to approximately 200° C. (past the melting pointof Form A) at a heating rate of 10° C. per minute. The molten cilostazolwas cooled to approximately 0° C. at a cooling rate of approximately 10°C. per minute. The cooled cilostazol was reheated from 0° C. to 120° andheld for five minutes. After holding for five minutes, the cilostazolwas cooled to 0° C. at a rate of 10° C. per minute.

[0100] The cilostazol was reheated in an undisturbed state by DSC from0° C. to 200° C. at 10° C. per minute. Two endotherms of melt wereobserved at approximately 138° C. (Form B) (onset at about 135° C.) and161° C. (Form A) (onset at about 159° C.) in a heat of enthalpy ratio ofapproximately 60:40, respectively, with the relative amount of Form Band Form A further variable on the heat of enthalpy of each polymorphicform.

EXAMPLE 5 Preparation of a Combination of Form A of Cilostazol, Form Bof Cilostazol and Form C of Cilostazol

[0101] A sample of approximately 5 mg of Form A cilostazol was placed ina vented, sealed aluminum holder and placed in a DSC furnace under anitrogen purge of 40 milliliters per minute, the sample was heated froma temperature of 30° C. to approximately 200° C. (past the melting pointof Form A) at a heating rate of 10° C. per minute. The molten cilostazolwas cooled to approximately 0° C. at a cooling rate of approximately 10°C. per minute. The cooled cilostazol was reheated from 0° C. to 110° C.,and held at 110° C. for 30 minutes. After holding the sample for 30minutes at 110° C., the cilostazol was cooled to 0° C. at a rate of 10°C. per minute.

[0102] The cilostazol was reheated in an undisturbed state by DSC from0° C. to 200° C. at 10° C. per minute. Three endotherms of melt wereobserved at approximately 138° C. (onset at about 136° C.) (Form B),149° C. (onset at about 147° C.) (Form C) and 161° C. (onset at about159° C.) (Form A) in a heat of enthalpy ratio of approximately 80:20:10,respectively, with the relative amount of Form B, Form C and Form Afurther variable on the heat of enthalpy of each polymorphic form.

EXAMPLE 6 Preparation of Form B: Form C (About 90:10)

[0103] A sample of approximately 7 mg of Form A of cilostazol was placedin a vented, sealed aluminum holder and placed in a DSC furnace. Under anitrogen purge of 40 milliliters per minute, the sample was heated froma temperature of 30° C. to a temperature of approximately 200° C. (pastthe melting point of Form A) at a heating rate of 10° C. per minute. Themolten cilostazol was cooled within the furnace to approximately 0° C.at a cooling rate of approximately 10° C. per minute. The cooledcilostazol was reheated from 0° C. to 130° C., and held at 130° C. forfive minutes. After holding the cilostazol at 130° C. for the fiveminutes, the cilostazol was cooled to 0° C. at a rate of 10° C. perminute. The cilostazol was then reheated in an undisturbed state by DSCat a rate of 10° C. per minute to a final temperature above 170° C. Thesample showed an endothermic peak for Form B of cilostazol atapproximately 138° C. (onset at about 135° C.) with a minor peak at 149°C. (onset at about 147° C.) which relates to Form C. The peaks show aForm B to Form C peak area ratio of approximately 90:10, respectively,with the relative amount of Form B to Form C further variable on theheat of enthalpy of each polymorphic form.

EXAMPLE 7 Preparation of Pure Form B of Cilostazol

[0104] A sample of approximately 8 mg of Form A of cilostazol was placedin a vented, sealed aluminum holder and placed in a DSC furnace. Under anitrogen purge of 40 milliliters per minute, the sample was heated froma temperature of 30° C. to approximately 200° C. (past the melting pointof Form A) at a heating rate of 10° C. per minute. The molten cilostazolwas cooled within the furnace to approximately 0° C. at a cooling rateof approximately 10° C. per minute. The cooled cilostazol was reheatedfrom 0° C. to 120° C. The cilostazol was cooled to 0° C. at a rate of10° C. per minute. The cilostazol was then reheated in an undisturbedstate by DSC at a rate of 10° C. per minute to a final temperature above170° C. The sample showed an endothermic peak for Form B of cilostazolat approximately 139° C. (onset at about 136° C.) with a minor peak at147° C. (onset at about 149° C.) which relates to Form C.

EXAMPLE 8 Preparation of Form B: Form C Cilostazol (About 66:34)

[0105] A sample of approximately 8 mg of Form A of cilostazol was placedin a vented, sealed aluminum holder and placed in a DSC furnace. Under anitrogen purge of 40 milliliters per minute, the sample was heated froma temperature of 30° C. to approximately 200° C. (past the melting pointof Form A) at a heating rate of 110° C. per minute. The moltencilostazol was cooled within the furnace to approximately 0° C. at acooling rate of approximately 10° C. per minute. The cooled cilostazolwas reheated from 0° C. to 1 10° C. The cilostazol was then cooled to 0°C. at a rate of 10° C. per minute. The cilostazol was then reheated inan undisturbed state by DSC at a rate of 10° C. per minute to a finaltemperature above 170° C. The sample showed an endothermic peak for FormB of cilostazol at approximately 138° C. (onset at about 135°) with aminor peak at 149° C. (onset at about 147° C.) which relates to Form C.The peaks show a Form B to Form C peak area ratio of approximately66:34, respectively, with the relative amount of Form B to Form Cfurther variable on the heat of enthalpy of each polymorphic form.

EXAMPLE 9 Preparation of Form B: Form C Cilostazol (About 92:8)

[0106] A sample of approximately 7 mg of Form A of cilostazol was placedin a vented, sealed aluminum holder and placed in a DSC furnace. Under anitrogen purge of 40 milliliters per minute, the sample was heated froma temperature of 30° C. to a temperature of approximately 200° C. (pastthe melting point of Form A) at a heating rate of 10° C. per minute. Themolten cilostazol was cooled within the furnace to approximately 0° C.at a cooling rate of approximately 10° C. per minute. The cooledcilostazol again was heated from 0° C. to 130° C., and held at 130° C.for 30 minutes. After holding the cilostazol at 130° C. for 30 minutes,the cilostazol was cooled to 0° C. at a rate of 10° C. per minute. Thecilostazol was then reheated in an undisturbed state by DSC at a rate of10° C. per minute to a final temperature above 170° C. The sample showedan endothermic peak for Form B of cilostazol at approximately 139° C.(with a minor peak at 149° C. which relates to Form C. The peaks show aForm B to Form C peak area ratio of approximately 92:8, respectively,with the relative amount of Form B to Form C further variable on theheat of enthalpy of each polymorphic form.

EXAMPLE 10 Preparation of Form B: Form C Cilostazol (About 87:13)

[0107] A sample of approximately 5 mg of Form A of cilostazol was placedin a vented, sealed aluminum holder and placed in a DSC furnace. Under anitrogen purge of 40 milliliters per minute, the sample was heated froma temperature of 30° C. to approximately 200° C. (past the melting pointof Form A) at a heating rate of 10° C. per minute. The molten cilostazolwas cooled within the furnace to approximately 0° C. at a cooling rateof approximately 10° C. per minute. The cooled cilostazol was reheatedfrom 0° C. to 100° C., and held at 100° C. for five minutes. Afterholding the cilostazol for the five minutes, the cilostazol was cooledto 0° C. at a rate of 10° C. per minute. The cilostazol was thenreheated in an undisturbed state by DSC at a rate of 10° C. per minuteto a final temperature above 170° C. The sample showed an endothermicpeak for Form B of cilostazol at approximately 138° C. (onset at about135° C.) with a minor peak at 149° C. (onset at about 147° C. whichrelates to Form C. The peaks show a Form B to Form C peak area ratio ofapproximately 87:13, respectively, with the relative amount of Form B toForm C further variable on the heat of enthalpy of each polymorphicform.

EXAMPLE 11 Preparation of Form B: Form C Cilostazol (About 83:17)

[0108] A sample of approximately 6 mg of Form A of cilostazol was placedin a vented, sealed aluminum holder and placed in a DSC furnace. Under anitrogen purge of 40 milliliters per minute, the sample was heated froma temperature of 30° C. to approximately 200° C. (past the melting pointof Form A) at a heating rate of 10° C. per minute. The molten cilostazolwas cooled within the furnace to approximately 0° C. at a cooling rateof approximately 10° C. per minute. The cooled cilostazol was reheatedfrom 0° C. to 120° C., and held at 120° C. for 30 minutes. After holdingthe cilostazol at 120° C. for 30 minutes, the cilostazol was cooled to0° C. at a rate of 10° C. per minute. The cilostazol was then reheatedin an undisturbed state by DSC at a rate of 10° C. per minute to a finaltemperature above 170° C. The sample showed an endothermic peak for FormB of cilostazol at approximately 139° C. (onset at about 136° C.) with aminor peak at 149° C. (onset at about 147° C. which relates to Form C.The peaks show a Form B to Form C peak area ratio of approximately83:17, respectively, with the relative amount of Form B to Form Cfurther variable on the heat of enthalpy of each polymorphic form.

EXAMPLE 12 Hot Stage Microscopy

[0109] A sample of Form A of cilostazol was placed on a glass slide andinserted into a hot stage microscope furnace. Hot stage microscopyprovides an analytical technique that allows for heat manipulation ofthe cilostazol sample while visual observing changes utilizing amicroscope apparatus. Samples of Form A cilostazol were heated toapproximately 170° C. and held until visually melted, then cooled byremoving the glass slide and placing it on a laboratory bench or othersuitable place to cool in an area free of potential contamination. Thesample was then heated under various conditions involving varyingheating rate (HR), maximum temperature (70° C., 80° C., 90° C. and 100°C.) and hold times (T), XRD was performed on each sample to monitor thedegree of crystallinity as well as crystalline forms present.

[0110] At 70° C.: a heating rate 1 degree per minute held for 5 minutesresulted in amorphous cilostazol; amorphous with about 5% Form B (HR=2,T=5); amorphous (HR=5, T=5); amorphous with about 5% Form B (HR=2, T=5);amorphous with about 20% Form B (HR=2, T=15); amorphous with about 60%Form B (HR=2, T=30); and trace amount of amorphous with about 95% Form B(HR=2, T=45).

[0111] At 80° C.: about 100% Form B (HR=1, T=5); about 80% Form B withabout 20% Form A (HR=2, T=5); about 100% Form B with trace amorphous(HR=5, T=15); about 40% Form B with about 60% Form A (HR=2, T=2); about20% Form B with about 80% Form A (HR=2, T=15); about 5% Form B withabout 95% Form A (HR=2, T=30); and about 100% Form A (HR=2, T=45).

[0112] At 90° C.: about 100% Form A (HR=1, T=5); about 95% Form B andtrace of Form A (HR=2, T=5); about 80% Form B (HR=5, T=5); about 95%Form B and trace Form A (HR 2, T=5); about 100% Form A (HR=2, T=15);about 100% Form A (HR=2, T=30); and about 100% Form A (HR=2, T=45).

[0113] At 100° C.: Form A with trace of Form B (HR=1, T=5); about 100%Form A (HR=2, T=25); and about 50% Form A and about 50% Form B (HR=5,T=5).

[0114] Hot stage microscopy was performed to provide an indication ofthe trends of the solid state transformations of the cilostazol. If analternative sample holder is used instead of glass (e.g., aluminum) thecooling process will need to be altered to avoid stress to the amorphoussample which will create nucleation sites that cause Form A topreferentially form upon reheating. Formulation 1 Hard gelatin 50 mgcapsules are prepared using the following ingredients: Quantity(mg/capsule) active ingredient(s) 50 ethanedioate starch, dried 200magnesium stearate 10 Total 260

[0115] The above ingredients are mixed and filled into hard gelatinCapsules in 260 mg quantities. Formulation 2 A 100 mg tablet is preparedusing the ingredients below: Quantity (mg/tablet) active ingredient(s)100 cellulose, microcrystalline 400 silicon dioxide, fumed 10 stearicacid 5 Total 515

[0116] The components are blended and compressed to form tablets eachweighing 515 mg. Formulation 3 Tablets each containing 50 mg of activeingredient are made as follows: active ingredient 50 mg starch 45 mgmicrocrystalline cellulose 35 mg polyvinylpyrrolidone 4 mg (as 10%solution in water) sodium carboxymethyl starch 4.5 mg magnesium stearate0.5 mg talc 1 mg Total 140 mg

[0117] The active ingredient, starch and cellulose are passed through aNo. 45 mesh U.S. sieve and mixed thoroughly. The solution ofpolyvinylpyrrolidone is mixed with the resultant powders which are thenpassed through a No. 14 mesh U.S. sieve. The granules so produced aredried at 50° C. and passed through a No. 18 mesh U.S. sieve. The sodiumcarboxymethyl starch, magnesium stearate and talc, previously passedthrough a No.60 mesh U.S. sieve, are then added to the granules which,after mixing, are compressed on a tablet machine to yield tablets eachweighing 140 mg. Formulation 4 Capsules each containing 50 mg ofmedicament are made as follows: active ingredient 50 mg starch 59 mgmicrocrystalline cellulose 59 mg magnesium stearate 2 mg Total 170 mg

[0118] The active ingredient, cellulose, starch and magnesium stearateare blended, passed through a No. 45 mesh U.S. sieve, and filled intohard gelatin capsules in 170 mg quantities.

[0119] The examples and embodiments as set forth in the detaileddescription are for illustrative purposes only and do not limit thescope of the invention.

What is claimed is:
 1. A process for preparing Form B of cilostazol,comprising the steps of: melting a cilostazol starting material; coolingthe melted cilostazol; and, heating the cooled cilostazol sufficient toinduce a cold crystallization to Form B of cilostazol.
 2. The process ofclaim 1, wherein the step of cooling the melted cilostazol comprises atemperature at or below about the glass transition temperature.
 3. Theprocess of claim 1, further comprising the step of: recooling the heatedcilostazol.
 4. The process of claim 2, further comprising the step of:recooling the heated cilostazol.
 5. Form B of cilostazol prepared by theprocess of claim
 1. 6. Form B of cilostazol prepared by the process ofclaim
 2. 7. Form B of cilostazol prepared by the process of claim
 3. 8.Form B of cilostazol prepared by the process of claim 4.